This invention relates to a perfected sintering machine specifically designed for the manufacture of components for tools and the like.
The invention also relates to a method of operation. Unlike known systems, the invention provides for pressure and heat to be applied to the material not at continually increasing values, but at intervals in accordance with a preset curve.
The various functions of the apparatus are electronically controlled by computer on the basis of data supplied by the control instruments which constantly monitor the plate movements and die temperature.
In the manufacture of sintering tools the powder used to make the part in question is introduced into a die and subjected to high temperature and pressure for a period of time which depends on the size of the object, the material used, etc.
This melts the surface of the granules to form a solid, compact whole.
Known types of sintering apparatus basically comprise a hydraulic press, electrical systems designed to heat the plates which compress the material in the die, and systems which eliminate heat in order to cool the die partially before removal.
The plates generally consist of several parts. One part, generally made of copper, is fixed to a mobile support or a machine structure, and the other, made of graphite or steel, comes into contact with the die.
This system is necessary because the part in contact with the die reaches extremely high temperatures which it must resist without buckling, while the outer part, in contact with the machine casing or the mobile support, must have high electrical conductivity and be cooled so that the heat developed at the die does not reach and damage the other parts of the machine.
This system, though necessary, also presents considerable drawbacks because the contact surface between the outer and inner plates rapidly oxidizes, preventing the passage of current and requiring frequent stoppages of the operating cycle during the day so that the plate can be cleaned.
This oxidation also causes wear on the contact surfaces between the two plates, which therefore require fairly frequent replacement.
A further drawback of known types of apparatus is that cooling of the various parts of the machine is not always efficient, as the coolant is used to eliminate heat from parts (such as the plates and the transformer) which operate at very different temperatures and therefore require different coolant flows.
Finally, in known machines the pressure and temperature are gradually, continuously increased until the maximum value is reached, after which the die cooling stage beings, and this also often leads to imperfect results.
The sintering machines in current use are basically rather imprecise and present a series of defects which produce results that are not always accurate and increase production time, thereby affecting the cost of the end product.